Emperor penguins thrive in an icebound world lethal to most life forms. Using ingenuity and endurance, a La Jolla researcher is trying to figure out how they do it.

INACCESSIBLE ISLAND, ANTARCTICA — The Emperor penguins, rising from the depths, levitate into the blue glow of an air hole in the ice.

No single creature more embodies the popular image of Antarctica than these droll birds dressed by nature for every formal occasion. Yet remarkably little is known about their behavior and biology.

The Emperors' captivating underwater behavior while foraging in what may be the planet's last unspoiled sea is a wonder normally denied to naturalists. The water in which they gambol is cold enough to quickly kill an unprotected human. An 8-foot-thick crust of ice hides the birds' activities from the surface.

But in a cramped glass observation chamber suspended a dozen feet beneath the sea ice that girdles Antarctica, a wiry field biologist from La Jolla named Gerald Kooyman has opened a unique window into one of the planet's most inaccessible habitats.

No sooner does the first Emperor crawl out of the water onto the surface of the ice than an observer crouched below in the chamber can see the streamlined silver shadows of half a dozen other penguins swim into view. One sports a small computerized depth gauge on its rump. Another has a catheter tucked under its left wing.

The underwater song of a lovesick seal--an eerie aria of trills, glissandos and percussive clicks--drifts across the sluggish currents and resonates in the chamber.

Kooyman, a University of California research professor at the Scripps Institution of Oceanography, is seeking to understand how penguins thrive under conditions that are lethal to most life forms.

The underwater chamber, like the use of special depth gauges and catheters that measure the diving bird's changing blood chemistry, are techniques the 60-year-old naturalist has improvised in a life devoted to the study of what may be the world's most unusual bird.

The Emperors of Antarctica dive deeper and longer than any other bird into Earth's coldest waters. No other animal breaks so many of the rules that govern life in Antarctica, an icebound vastness larger than North America.

In a manner that makes them seem neither fish nor fowl, the sleek, flightless Emperors are equally at home in two of Earth's most inhospitable environments.

No other bird dives deeper than the Emperor, as much as 1,500 feet for as long as 18 minutes. They also thrive on the surface under conditions that would doom almost any other animal--from temperatures that drop to 100 degrees below zero to winds that top 200 mph.

"The biology of this is still very much a foreign frontier," Kooyman says.

As he talks, he struggles to keep his balance in a wind blowing with enough bluster to flatten the tents pitched on the ice. Nearby, the penguins huddle together comfortably.

Last Pristine Ocean

The penguins' well-being is so closely linked to the ice they inhabit that their numbers rise and fall depending on the condition and extent of the sea ice each year. That may make the birds especially sensitive barometers of global warming and climate change, researchers say.

Until recently, most researchers thought that penguins of all kinds were safe from human disturbances or environmental changes. Now some researchers are worried about a disturbing decline among the penguins of Antarctica.

In the past four years, the numbers of several species in other parts of the continent have plummeted. No one knows whether the decline is caused by a succession of unusually warm winters, a drop in the population of the shrimp-like crustaceans on which they feed, or stress caused by the growing influx of tourists visiting crowded nesting colonies.

The Ross Sea, where Kooyman conducts his research, may be their last undisturbed haven.

There are 30 Emperor colonies on the continent, home to a quarter-million birds. Seven are around the Ross Sea, where Kooyman has counted about 70,000 Emperor breeding pairs. Only one of the seven colonies was known at the turn of the century. Most were discovered in the 1960s. The newest--which was home to 8,000 Emperor chicks last year--was discovered by Kooyman in 1993. It took him five years to find it.

"The Ross Sea is a pristine ocean and, as far as I know, it is the only pristine ocean in existence," Kooyman says. "It is the only one where there has been no commercial exploitation and no severe environmental problems."

In the short run, Kooyman and his colleagues are eager to simply understand the animals themselves. But they also hope that what they can learn about how penguins survive without oxygen for extended periods might one day lead to medical applications for humans.

"We have a remarkable opportunity here that we have nowhere else."

Antarctic Laboratory

To understand the Emperors, Kooyman has made all of Antarctica his laboratory.

Working under the auspices of the National Science Foundation, he has been coming here for so many years that a mountain peak is named after him, so many years that his hair is now the color of snow.